1833年到1855年間由聖塔安那執政（Santa Anna），他的政治生涯幾經起伏更迭，下朝再上朝，共有11次之多。這段期間墨西哥和美國幾番激戰，最後割讓了德州、新墨西哥州和亞歷桑那州給美國。 1855年，曾被聖塔安那放逐的政敵傑瑞茲（Benito Juarez）結合強大的反對勢力，把執政十多年的獨裁者趕下臺。傑瑞茲屬自由新政派，在位時推動新法，取消天主教會和軍隊的免責權。這些保守勢力的反彈導致改革戰爭（War of the Reform），這是有史以來最血腥的一次內戰，但最終結果還是代表自由派的傑瑞茲再度贏得選舉。再度執政的傑瑞茲雖然面對國內外動蕩情勢，仍致力於基礎建設、推展教育，慢慢使墨西哥的政治社會環境步上正軌。
In 1855, Santa Anna, who had become leader one more time, was overthrown by the liberals, in what was called the Revolution of Ayutla. The moderate liberal Ignacio Comonfort became president. The Moderados tried to find a middle ground between the nation's Liberals and Conservatives.
The 1857 Constitution
During Comonfort's presidency, a new Constitution was drafted. The Constitution of 1857 retained most of the Roman Catholic Church's Colonial era privileges and revenues, but, unlike the earlier constitution, did not mandate that the Catholic Church be the nation's exclusive religion. Such reforms were unacceptable to the leadership of the clergy and the Conservatives. Comonfort and members of his administration were excommunicated, and a revolt was then declared.
The War of Reform
This led to the War of Reform, from December 1857 to January 1861. This civil war became increasingly bloody and polarized the nation's politics. Many of the Moderates came over to the side of the Liberals, convinced that the great political power of the Church needed to be curbed. For some time, the Liberals and Conservatives had their own governments, the Conservatives in Mexico City and the Liberals headquartered in Veracruz. The war ended with Liberal victory, and Liberal president Benito Juárez moved his administration to Mexico City.
